Mixing device

ABSTRACT

An elongated housing has a substantially horizontal longitudinal axis and is arranged to accommodate a body of liquid. A rotatable shaft extends through the housing along the axis and carries a plurality of mixing elements for rotation with it; each mixing element is disk-shaped and configurated so as to axially draw in and peripherally expel the ambient liquid. Gas inlets are provided each of which is associated with one of the mixing elements in the region where the same axially draws in the ambient liquid.

United States Patent Mueller Oct. 29, 1974 MIXING DEVICE [76] Inventor: Hans Mueller, Alte Landstrasse 41s, "3" shap'm Mannedorf Zurich Asslstant Examiner-R. Penland Switzerland Attorney, Agent, or Firm-Michael S. Striker [22] Filed: Dec. 11, 1972 [30] Foreign Application Priority Data Dec. 10, 1971 Switzerland 18136/71 Jan. 28, 1972 Switzerland 1333/72 Feb. 28, 1972 Switzerland 2689/72 [52] US. Cl. "195/142 195/139, 261/87 [51] Int. Cl Cl2b 1/14 [58] Field of Search 195/142, 139; 261/93, 87

[56] References Cited UNITED STATES PATENTS 3,460,810 8/1969 Mueller 261/93 X Appl. No.: 314,280

[5 7 ABSTRACT An elongated housing has a substantially horizontal longitudinal axis and is arranged to accommodate a body of liquid. A rotatable shaft extends through the housing along the axis and carries a plurality of mixing elements for rotation with it; each mixing element is disk-shaped and configurated so as to axially draw in and peripherally expel the ambient liquid. Gas inlets are provided each of which is associated with one of the mixing elements in the region where the same axially draws in the ambient liquid.

12 Claims, 5 Drawing Figures 1 MIXING DEVICE BACKGROUND OF THE INVENTION The present invention relates to a mixing device in general, and more particularly to a device for admixing gases with liquids, especially for the purpose of cultivating arobic microorganisms in liquid nutrient medium while supplying air, oxygen or other oxygencontaining gases.

Devices of this type are already well known. They are used, for instance, for the purpose of cultivating various microorganisms such as yeast, molds or the like, and should ideally be capable of admixing the liquid and gas so intimately that the organisms suspended in the nutrient medium, namely the liquid, can contact the oxygen and the nutrient in the liquid as directly as possible. At the same time, the supply of nutrients and the removal of reaction products should be maintained during the entire time during which a culture is accommodated in the mixing vessel housing.

The prior-art devices use vessels which accommodate the liquid and which are provided with agitating'or mixing instrumentalities; gas is introduced into the vessel and it is the purpose of the mixing instrumentalities to attempt to admix the gas with the liquid. Another type of construction supplies an arrangement which moves the liquid in form of a thin layer or vail in the housing, in order to obtain as large as possible an interface with the gas. The first-mentioned type of construction utilizes relatively rapidly rotating mixing instrumentalities and require a rather high supply of energy, not only for their rotation but also for the admission of the gas which is to be distributed, if the apparatus is intended for substantial capacities and if therefore a substantial amount of liquid is to be accommodated in it at any given time. This, in turn, means that if the desired degree of admixture of gas and liquid is to be obtained, the housing must be relatively narrow in cross section and this causes a high hydrostatic counter pressure which must be overcome when the gas is introduced; hence, the high energy requirement in connection with the introduction of the gas.

It has been proposed to reduce the hydrostatic counter pressure and therefore to ease the introduction of the gas, by making the vessel rather wide and lower. This, however, requires a quite complicated distributing arrangement in order to assure that the gas will be admixed with the liquid in sufficiently fine distribution. Moreover, such a configuration for the mixing vessels requires more floor space which is often at a premium.

To overcome the aforementioned disadvantages the art has proposed to orient the housing of the mixing vessel horizontally, thereby requiring a comparatively long but narrow amount of floor space, and reducing the hydrostatic counter pressure which opposes the introduction of the gas into the housing. However, this proposal also has not been entirely satisfactory because there is a relatively small amount of liquid accommodated in this type of vessel. and because the interface between the gas and liquid is relatively small. A rather better construction of this type proposes such a vessel which is upright and in which agitating instrumentalities are mounted on a common rotatable shaft which in turn is surrounded. together with the agitating instrumentality by a tubular guide baffle. which has at the level of the respective instrumentalities small and dispersing openings and intermediate the instrumentalities large draw-in or suction openings. The difficulty here is that the high energy requirement for introducing the gas into the vessel, and in order to overcome the hydrostatic counter pressure of the liquid, that was mentioned with respect to the first described prior-art constructions obtains for this latter type of construction also. The seemingly obvious answer, namely to have the housing of the vessel so arranged that its longitudinal axis is horizontal rather than vertical, does not work because heretofore it has not been possible to achieve a proper movement of the liquid and the gas axially of a vessel which is so oriented, and at the same time to obtain the desired degree of admixture.

SUMMARY OF THE lNVENTlON It is, accordingly, an object of the present invention to provide an improved apparatus of the type here under discussion which is not possessed of the aforementioned disadvantages.

More particularly it is an object of the present invention to provide for such an improved apparatus which is capable of achieving a highly satisfactory and very intimate admixture of gas and liquid, while requiring only a small amount of energy for the introduction of the gas into the vessel and into the liquid accommodated therein.

Another object of the invention is to provide such an apparatus which is relatively simple in its construction and therefore inexpensive to produce.

ln keeping with these objects, and others which will become apparent hereafter, one feature of the invention resides in a device for mixing liquid and gas, especially for mixing gaseous fluid into liquid nutrients in fermentation processes. The device comprises an elongated housing having a substantially horizontal longitudinal axis and adapted to accommodate a body of liquid. A rotatable shaft extends in the housing along the axis, and a plurality of mixing elements is mounted on the shaft for rotation therewith, each being configurated as a disk-shaped element which axially draws in and peripherally expels the ambient liquid. A plurality of gas inlets are provided, each of which is associated with one of the mixing elements and is located in the region where the same axially draws in the ambient liquid.

lt is particularly advantageous, although not absolutely necessary, if the shaft and the admixing elements are surrounded by a guide baffle of tubular configuration, provided intermediate the respective axially spaced mixing elements with larger inlet or suction openings through which the elements can draw fluid, and in the region of the periphery of the elements with smaller dispersion openings through which the elements can expel a mixture of liquid and gas to the outside of the baffle.

It has been found that the energy required for driving the shaft and the mixing elements in rotation can be reduced if the dispersing openings are of different size at different points of the guide baffle, so that some of these openings are capable of serving less for dispersing purposes than for the circulation of the liquid between the inside and the outside of the guide baffle in the housing.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however,

both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a somewhat diagrammatic axial section of an apparatus according to the present invention;

FIG. 2 is a fragmentary section of detail view, on an enlarged scale, of the embodiment illustrated in FIG. 1;

FIG. 3 is a section taken on line A-B of FIG. 2; and

FIG. 4 is a section taken on line CD of FIG. 2 and FIG. is a view similar to FIG. 4, but of a further embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing in detail with reference to FIGS. l4 it is pointed out that the illustrated apparatus shows a combination of several structural features which can all be provided in one and the same apparatus as illustrated, or only some of which can be provided. This will become clearer from a discussion of the drawing.

In FIG. I it will be seen that the housing is designated with reference numeral 1. It is intended to accommodate a liquid, such as a nutrient medium, and is surrounded by a jacket 2 in order to make it possible to heat and/or cool the housing 1 by circulation of an appropriate heat exchange fluid. The longitudinal axis of the housing 1 is arranged substantially horizontally and extending along it is a shaft 3 which can be driven from motor 4 via a belt drive 5 or similar means. It is, however, expressly pointed out that the shaft 3 need not be located directly on the longitudinal axis of the housing 1, and that other means for driving it in rotation can also be employed. Naturally, in the illustrated embodiment the motor 4 and the belt drive 5 are located outside the housing 1, engaging a portion of the shaft which extends to the exterior thereof.

The shaft carries a plurality of mixing instrumentalities or elements which are axially spaced from one another along the shaft, advantageously at equal dis tances, and which are so constructed that they will draw in liquid in axial direction of the shaft, and will expel it in peripheral direction, that is transversely of the shaft.

The drawing shows different possibilities of construction for the mixing elements, and such different possibilities may be provided in one or the same apparatus or only one or to or more together may be provided in one and the same apparatus. It will be seen that the instrumentality 7 has paddles which are annularly shielded in axial direction, or which are open as indicated at reference numeral 7". Another possibility is designated with reference numeral 8, showing the paddles open at one side and closed at the other. In any case, the mixing instrumentalities are surrounded in this embodiment by the tubular guide baffle 6 provided with openings of various different sizes. Large openings 9 for drawing in liquid admixed with gas by the mixing instrumentalities are provided intermediate the adjacent mixing instrumentalities, and in the vicinity of the peripheral of the individual mixing instrumentalities the guide baffle is provided with smaller openings 10 and larger slot-shaped openings 1].

A conduit 13 is provided through which the gas or gases to be admixed with the liquid contents of the housing I are supplied. It is provided with several branches which extend through the openings 9 in the baffle 6 and which are provided with inlets in form of nozzles 14 which are located axially in the vicinity of the respective mixing instrumentalities. An inlet 19 is provided communicating with the housing I for admission of the liquid therein, and an outlet 20 permits the removal of the liquid; it should be noted that the inlet and outlet are located at opposite axial ends of the housing I so that the liquid admitted will sequentially pass through the regions of effectiveness of the several mixing instrumentalities mounted on the common drive shaft 3. This means that the reaction, such as a fermentation process, can be carried out continuously or, at the option of an operator, in batches. Recirculation can be achieved via a pump (not shown) whose suction side is connected with the outlet 20 and whose pressure side is connected with the inlet 19. Spent or excess gas is expelled through the outlet 18 by the rotating foam separator I7 which is driven by a motor 16 and accommodated in the tubular extention 15 which extends upwardly from the housing 1 and communicates with the same as shown.

As mentioned earlier, different size openings may be provided in the guide baffle 6. The various possibilities which have been shown in FIG. 1 can be all provided in one and the same apparatus, or they can be singly or in any desired combination provided in an apparatus. As illustrated, only fine openings are provided in the baffle in the region of the mixing instrumentalities 7, fine openings and downwardly enlarged slot-shaped openings are provided in the region of the instrumentalities 7', fine openings at one side of the axis of rotation of the shaft 3 and larger slot-shaped openings at the other side of the axis of rotation are provided in the region of the instrumentalities 7, and as shown in FIGS. 1 and 3 the baffle may be provided in the region of the instrumentalities 8 with small openings over its entire circumference but at one point with a coaxially arranged slot 12. It is also possible to make the shaft 3 hollow and to supply the gas through it into the housing 1, in which case the shaft would of course have to provided with openings which, according to the invention, would be located in the region of the individual mixing instrumentalities.

Two of the mixing instrumentalities are illustrated with a portion of their surrounding guide baffle in FIG. 2 on an enlarged scale. It will be seen that above the center line the guide baffle is shown in elevation and below it in section. The mixing instrumentalities are provided with radial paddles 21 which are mounted on a center hub 22 and are shielded in axial direction by a ring member 23. Thus, the axially drawn-in liquid is guided within this thus-constructed paddle wheel. At the left the guide baffle is provided only with a plurality of small dispersing openings 10, and has at one location a longitudinally extending slot-shaped opening 12 the boundary edges of which are so bevelled that liquid which is peripherally ejected or expelled by the instrumentality 8 can tangentially leave the guide baffle, whereas over the remainder of the periphery of the guide baffle it is caused to pass through the small openings I0, as shown in section in FIG. 3.

FIG. 2 shows at the right-hand side another mixing instrumentality whose construction is identical with the one shown at the left-hand side. Here, however, the guide baffle is provided with openings arranged and dimensioned differently from those associated with the instrumentality at the left-hand side of FIG. 2. ln particular, the circumference of the guide baffle is provided over one axial half of the elongation of the instrumentality 8 with small dispersing openings 10, whereas over the other half of the axial elongation of the instrumentality 10 the guide baffle is provided in its periphery with large slot-shaped openings 11, with the expulsion of liquid through the openings 11 taking place in the manner indicated by the arrows in FIG. 4.

Depending upon the type of process to be carried out in the novel apparatus, and the characteristic of the contents of the housing, such as the viscosity, content of solid particles and the like, the openings 10 or the openings 11-12 might be favored. in other words, it may be desired to have more of the openings 10 and fewer of the openings 11, 12, or vice versa. What is important is that the various types of openings are provided in one and the same guide baffle so that the dispersion effect of ejected liquid and the shear effect of liquid ejected through the larger openings will take place simultaneously in the housing 1, in addition to the mixing and circulating effect obtained by the rotation of the mixing instrumentalities.

As previously pointed out, it is possible to arrange the shaft 3 with the mixing instrumentalities and the surrounding guide baffle transversely offset from the longitudinal axis of the housing 1, that is eccentrically, a solution which might be employed if a larger space is to be available for gases being introduced. This is somewhat diagrammatically shown in FIG. 5, which will require no other discussion because it is clearly selfexplanatory.

lt will be appreciated that it may be advantageous to make it possible to vary the sizes of the openings 10, 11 and 12 (and in particular of any or all of these openings) from the exterior of the housing 1, to be readily able to influence the progress of a process being carried out. For this purpose, suitable means may be provided, and in fact it is possible to have such means be operatively associated with the drive motor 4 so that they will be automatically controlled in dependence upon the amount of current which is being drawn by the drive motor. In other words, as the resistance offered to rotation of the instrumentalities on the shaft 3 varies, in dependence upon different conditions of the liquid and gas mixture in the housing 1, the amount of current drawn by the motor 4 will also vary and this can be used as a determinator which automatically triggers the means for varying the size of the openings in the guide baffles. Such arrangements can be used to particular advantage in case of batchwise operation. in which the characteristics of the liquid-gas mixture change as the process progresses. or else in the case of test installations in order to be able to provide an accommodation to different applications.

it will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a mixer, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A device for mixing liquid and gas, especially for mixing gaseous fluid into liquid nutrients in fermentation processes, comprising an elongated housing having a substantially horizontal longitudinal axis, and adapted to accommodate a body of liquid; a rotatable shaft extending in said housing along said axis; a plurality of mixing elements mounted on said shaft for rotation therewith and each configured as a disc-shaped element which axially draws in and peripherally expells the ambient liquid; said elements being spaced axially of said shaft and having respective peripheries; a tubular guide baffle surrounding said shaft and elements in said housing and having larger suction openings located intermediate the respective elements for said mixing elements to draw fluid therethrough, and smaller dispersing openings in the region of the respective periphery for discharge of a gas and liquid mixture to the exterior of said baffle; a conduit extending along said horizontal axis and comprising a plurality of branches extending through axially spaced openings in said baffle; and a plurality of gas inlets, each associated with one of said branches and one of said mixing elements, and located in the region where said mixing elements axially draw the ambient liquid.

2. A device as defined in claim 1, said elements being spaced axially of said shaft and having respective peripheries; and further comprising a tubular guide baffle surrounding said shaft and elements in said housing and having larger suction openings located intermediate the respective elements for the same to draw fluid therethrough, and smaller dispersing openings in the region of the respective periphery for discharge of a gas and liquid mixture to the exterior of said baffle.

3. A device as defined in claim 2; further comprising gas conduits extending through said suction openings and provided with said gas inlets.

4. A device as defined in claim 1, said shaft being hollow and arranged to communicate with a source of gas, and said gas inlets being provided in said shaft so as to admit gas from said inlets into said housing.

5. A device as defined in claim 2, wherein the dimensions of at least some of said openings are different in different axial regions of said baffle.

6. A device as defined in claim 2, wherein said shaft and fluid baffle are non-concentric with reference to said axis.

'7. A device as defined in claim 2', and further comprising means for varying the size of at least some of said openings from the exterior of said housing.

8. A device as defined in claim 7; further comprising an electromotor associated with said shaft for rotating the same; and wherein said means for varying the size of at least some of said openings is operatively associated with said motor and responsive to fluctuations in the amount of electrical energy drawn by the same.

9. A device as defined in claim 1, further comprising a foam separator communicating with said housing.

10. A device as defined in claim I, wherein said conduit extends exteriorly of said housing.

11. A device for mixing liquid and gas, especially for mixing gaseous fluid into liquid nutrients in fermentation processes, comprising an elongated housing having a substantially horizontal longitudinal axis, and adapted to accommodate a body of liquid; a rotatable shaft extending in said housing along said axis; at least one mixing element mounted on said shaft for rotation therewith and configured as a disc-shaped element which axially draws in and peripherally expels the ambient liquid; said element being spaced axially of said shaft; a tubular guide baffle surrounding said shaft and element in said housing; a conduit extending along said horizontal axis and comprising a plurality of branches extending through axially spaced openings in said baffle; and at least one gas inlet associated with said mixing element, and located in the region where said mixing element axially draw the ambient liquid.

12. A device as defined in claim 11 and wherein said guide baffle has at least one larger slot-shaped opening through which said element draws fluid, and a plurality of smaller dispersion openings for said element to discharge a gas and liquid mixture therethrough and to the exterior of said guide baffle. 

1. A DEVICE FOR MIXING LIQUID AND GAS, ESPECIALLY FOR MIXING GASEOUS FLUID INTO LIQUID NUTRIENTS IN FERMENTATION PROCESSES, COMPRISING AN ELONGATED HOUSING HAVING A SUBSTANTIALLY HORIZONTAL LONGITUDINAL AXIS, AND ADAPTED TO ACCOMODATE A BODY OF LIQUID; A ROTATABLE SHAFT EXTENDING IN SAID HOUSING ALONG SAID AXIS; A PLURALITY OF MIXING ELEMENTS MOUNTED ON SAID SHAFT FOR ROTATION THEREWITH AND EACH CONFIGURED AS A DISC-SHAPED ELEMENT WHICH AXIALLY DRAWS IN AND PERIPHERALLY EXPELLS OF SAID SHAF ENT LIQUID; SAID ELEMENTS BEING SPACED AXIALLY OF SAID SHAFT AND HAVING RESPECTIVE PERIPHERIES; A TUBULAR GUIDE BAFFLE SURROUND-
 2. A device as defined in claim 1, said elements being spaced axially of said shaft and having respective peripheries; and further comprising a tubular guide baffle surrounding said shaft and elements in said housing and having larger suction openings located intermediate the respective elements for the same to draw fluid therethrough, and smaller dispersing openings in the region of the respective periphery for discharge of a gas and liquid mixture to the exterior of said baffle.
 3. A device as defined in claim 2; further comprising gas conduits extending through said suction openings and provided with said gas inlets.
 4. A device as defined in claim 1, said shaft being hollow and arranged to communicate with a source of gas, and said gas inlets being provided in said shaft so as to admit gas from said inlets into said housing.
 5. A device as defined in claim 2, wherein the dimensions of at least some of said openings are different in different axial regions of said baffle.
 6. A device as defined in claim 2, wherein said shaft and fluid baffle are non-concentric with reference to said axis.
 7. A device as defined in claim 2; and further comprising means for varying the size of at least some of said openings from the exterior of said housing.
 8. A device as defined in claim 7; further comprising an electromotor associated with said shaft for rotating the same; and wherein said means for varying the size of at least some of said openings is operatively associated with said motor and responsive to fluctuations in the amount of electrical energy drawn by the same.
 9. A device as defined in claim 1, further comprising a foam separator communicating with said housing.
 10. A device as defined in claim 1, wherein said conduit extends exteriorly of said housing.
 11. A device for mixing liquid and gas, especially for mixing gaseous fluid into liquid nutrients in fermentation processes, comprising an elongated housing having a substantially horizontal longitudinal axis, and adapted to accommodate a body of liquid; a rotatable shaft extending in said housing along said axis; at least one mixing element mounted on said shaft for rotation therewith and configured as a disc-shaped element which axially draws in and peripherally expels the ambient liquid; said element being spaced axially of said shaft; a tubular guide baffle surrounding said shaft and element in said housing; a conduit extending along said horizontal axis and comprising a plurality of branches extending through axially spaced openings in said baffle; and at least one gas inlet associated with said mixing element, and located in the region where said mixing element axially draw the ambient liquid.
 12. A device as defined in claim 11 and wherein said guide baffle has at least one larger slot-shaped opening through which said element draws fluid, and a plurality of smaller dispersion openings for said element to discharge a gas and liquid mixture therethrough and to the exterior of said guide baffle. 